1. Field of the Invention
The present invention relates to a cutting machine (specifically a NC lathe or machining center) for performing various cuttings according to numerical control, and a control apparatus for the cutting machine.
Particularly, this invention relates to the control apparatus for the cutting machine in which a turret 1 rotates around a turret axis B (a B-axis) so that a cutting process can be performed at an arbitrary position (capable of indexing at the arbitrary position).
2. Related Art
(1) Modes of controlling a cutting edge of a cutting tool 2 in a conventional cutting machine are shown in FIGS. 8 and 9. FIG. 8 shows a mode in which a cutting is performed while the turret 1 is kept at a fixed angle. FIG. 9 shows a mode in which the turret 1 is rotated according to an outer configuration of a work to be cut. Respective positions of the cutting edge are represented by a0 to a3, and positions of the turret axis B are represented by b0 to b3.
The cutting tool 2 is usually controlled by controlling coordinates of the turret axis B. Here, in the mode as shown in FIG. 8, the coordinates of the turret axis B can be easily obtained by offsetting distances from the cutting edge to the turret axis B (Δx, Δz) out of the coordinates of the cutting edge.
However, there has been a problem that when an arc-shaped surface is cut while keeping the angle of the turret 1 in this manner, an angle between the cutting tool 2 and the work to be cut (a cutting angle β shown in the drawings) is not constant.
In case of performing a cutting with high precision, it is desirable to perform the cutting always at the same position of the cutting edge in a single cutting process. Here, the cutting edges at the cutting positions a0 and a2 are shown in enlarged views. At the cutting position a0 in the drawing, the cutting is performed by a left side of the cutting edge. On the other hand, at the cutting position a2 in the drawing, the cutting is performed by an underside of the cutting edge. In this manner, unless the cutting angle β is stabilized in the single cutting process, it will be difficult to cut precisely.
The cutting process as shown in FIG. 9 is in the mode in which the turret 1 is gradually rotated according to an outer configuration of the work to be cut. In this mode, the above described problem will not occur, because a fixed cutting angle β can be always maintained. However, in this case, it is necessary to obtain the coordinates of the turret axis B Considering the rotation of the turret 1, instead of simply offsetting from the coordinates of the cutting edge. For this reason, in the embodiment as shown in FIG. 9, there has been such a problem that when preparing a program, calculation of the coordinates of the turret axis B has been difficult.
Moreover, it would be necessary to develop a new control program in order to control movement of the turret on the basis of the coordinates of the cutting edge, and enormous cost and time would be required.